An association model with a cubic equation of state was adopted to calculate the solubilities of alkali metal chlorides in water vapor under high temperatures and pressures. The solubilities of sodium chloride (NaCl) and potassium chloride (KCl) were correlated by optimized association numbers and equilibrium constants. The correlated results represented well the experimental results. The logarithm of equilibrium constants show linear functions of reciprocal of the absolute temperature.